ActionScript 2.0 :: Dynamic Text Size Change Within MovieClip

I'm trying to change the text size in a dynamic text area within a (movie clip) button. For a couple of buttons I'd like to make certain text smaller, for example, to make the "vs" smaller in "A VS B". My buttons have dynamic text in them and the font is embedded and set at size 10 initially. The code I've got in my movie is as follows:

Code:
// define new text formatting
var minimenutext_txt:TextFormat = new TextFormat();
minimenutext_txt.size = 8;
avsb_txt = "A VS B";
avsb_txt.setTextFormat(3,4,minimenutext_txt);
// assign formatting to button dynamic text
btn1.btext.buttext.text = avsb_txt;

The text "A VS B" shows up in my button, but I can't seem to do anything to change the format. I've tried making it bold, italic, that kind of thing too - but no luck. Does the setTextFormat command only work with input dynamic text boxes? Is it being overruled somehow?